Electron discharge device



' 27, 1938. B.'J. THOMPQSON 2,141,673

I ELECTRON DISCHARGE DEVICE Filed Jan. 29, 1957 INVENTOR 1 BROWDER J. THOMPSON A ORNEY LII Patented Dec. '27, 1938 UNITED STATES ELECTRON DISCHARGE DEVICE- Browder J. Thompson, Basking Ridge, N. J., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application January 29, 1937, Serial No. 122,913

16 Claims.

My invention relates to electron discharge devices and has for its principal object the provision of an electron discharge device having novel characteristics, particularly a negative mutual conductance.

In the conventional tube having a cathode and anode and one or more grids positioned between the cathode and anode, one of which may be a control grid, as the control-grid voltage becomes more positive the plate current increases. In a tube made according to my invention as the grid voltage is made more positive the plate current decreases. Such a tube has many useful applications.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description'taken in connection with the accompanying drawing in which Figures 1 to 3 inclusive are schematic diagrams illustrating the theory upon which a tube made according to my invention is based, Figure 4 is a schematic diagram of an electron discharge device embodying my invention and its associated circuit, and Figure is a characteristic curve of the electron discharge device shown in Figure 4.

In an electron discharge device comprising a cathode, a grid and an anode in which the spacing betwen the grid and the anode-is large compared with the spacing between the grid and the cathode and with a high positive potential on the grid and a low positive potential on the plate, I have found that it is possible to cause the formation of a virtual cathode between the grid and the anode. By a virtual cathode is'meant a surface at a distance from the real cathode at which the electrons have substantially zero veloc ity and atleast some of them return to the oathode and others are drawnforward by any positive potential beyond the virtual cathode. The current flowing to a positive electrode beyond the virtual cathode is determined by the distance between the virtual cathode and the positive electrode and the potential of the positive electrode, just as in the case of a real cathode. By controlling the position of the virtual cathode I have been able to produce a novel'tube.

In Figure l the electron discharge device comprises cathode I6, positively biased grid II and anode I2, the grid I I being at a higher positive potential. In this arrangement a virtual cathode will be formed betweenthe positive grid II and the anode I2 as shown for example at V. C., if the spacing between grid and plate is great enough. In this arrangement the virtual cath ode cannot be formed closer to the positive grid than the distance between the grid II and the cathode III. In the case of space-charge-limited emission from the cathode "I, the position of the virtual cathode is nearly independent of the potential of grid II and therefore the current to the anode I2 is determined only by the anode potential. If, now, an additional grid I3 is placed between the positive grid I I and the cathode at the potential of the space before the addition of the grid, the position of the virtual cathode is unchanged. However, as the grid I3 is made less positive the virtual cathode moves away from the grid I I toward the anode I2 as shown at V. C., and therefore the current to the anode increases. Since the anode current increases as the grid I 3 is made more negative, there exists a negative mutual conductance between grid I3 and anode I2.

A tube of this structure exhibits this novel property and may be useful. However, because it is desirable to operate the grid I 3'at a negative potential, a very large space is required between the grid I I and the anode I 2 for the formation of a virtual cathode. The space required for the formation of a virtual cathode may be greatly reduced by the addition of a grid It, Figure 3, at approximately zero potential. If the grid I4 is at the same distance from grid I I as grid I3, the virtual cathode will be at substantially the same distance from the grid II as the true cathode III. Grid I3 will still show a negative mutual conductance with respect to the anode I2, if grid I4 is maintained at a constant potential.

In the structure of Figure 3 it is necessary to operate the anode I2 at a relatively low potential 5 if the virtual cathode is formed near the anode, as is required for high mutual conductance, because of the low plate resistance. Further, the amplification factor of such a structure is low. To produce a tube having the usual magnitudes of plate resistance and amplification factor and operating at usual anode voltages, a fourth grid is placed between the virtual cathode and the anode at a substantially zero potential.

This is shown in the arrangement shown in Figure 4. According to my invention this tube has a cathode I5, grids IS, IT, I8 and I9 and anode 20, the virtual cathode being formed between the third and fourth grids I8 and I9, the control grid I6 or the No. 1 grid determining the position of the virtual cathode in the space between these two grids. 'With a certain negative potential applied to grid I6 and decreasing the negative bias the virtual cathode is made to move away from the grid I9 toward grid I8 and as a result the plate current decreases. With increasing negative potential on grid I6 the virtual cathode moves toward grid I 9 and the anode current increases.

Ina tube made according to my invention proper spacing must be established between the various electrodes in order to form the virtual cathode between the third and fourth grids. In

the ideal case with parallel plane electrodes and grids I6, I8 and I9 operated at the potential of the cathode, a virtual cathode will be formed between grids I8 and I9 if the distance between grids I6 and I1 is equal to the distance between grids I1 and I8, and the distance between grids I8 and I9 is as great or greater than the distance between cathode I5 and grid I6, and further provided that grids I6 and I8 are of similar structure and potential may be made. A battery 23 may,

be used for biasin grid I6 negatively.

A satisfactory tube has been made with the ratio of the spacings between the cathode and the No. 1 grid, between the No. 1 and No.2 grids, be-

tween the No. 2 and No. 3 grids, between the No.

3 and No. 4 grids, and between the No. 4 grid and anode of the order of 1, 2, 2, 4, 2. It is also necessary that the No; 4 grid have a sufficiently fine mesh to shield the virtual cathode from the anode so that a high plate voltage can be used. For.

best operating results the voltages on the No. 1, No. 3 and No. 4 grids should be'zero or negative with respect to the cathode; With the arrangement described it is possible to use either the No; 1, No. 3 or No. 4 grid for control purposes, in which case the No. 3 or No. 4

positive mutual conductance. Two or more of these grids couldalso be used for control purposes.

An example ofatube made in accordance with my invention included a cathode having a diameter of .0445", an'elliptical No; 1 grid having a minor axis of .098" and a major axis of .121" wound with 23 '1?1 and using 4.1 elliptical No. 2 grid having a minor axis of .192" and a major axis of .216 with 32 TPI and using 5.1 mil wire, an elliptical No. 3 grid having a minor axis of .295"-and a major axis of .330" with 12 TPI and using 6.0 mil wire, and a No. 4 grid having a diameter of .500 with 30 TPI and using 5.0 mil wire, the plate diameter being .600. This tube operated very satisfactorily with the usual operating voltages applied to the No. 1 grid and anode.

A characteristic curve of such a tube is shown in Figure 5 and the'range WR, or working range,

is the range in which the tube is operated. Be- 7 cause of this characteristic it is possible to devise novel circuit schemes which are capable of making use of the unique characteristic of this tube.

One such circuit is a resistance coupled push-pull.

circuit fed from a single ended driver circuit, and using a conventional tube and a tube made according to my invention. Such a circuit, of course, is not possiblev with only conventional tubes. Another application of the tube is to an oscillator in which direct coupling can be had between the anode and grid instead of using coils forcoupling since the plate voltage is in phase with the grid voltage in atube made according to my invention.

A further possible application of a tube made according to my invention is to use the positive grid as the output electrode. Since the total cathode current is increasing with more positive inner grid potential and the plate current is degrids will have a mil wire, an r creasing, it follows that the positive grid current is increasing rapidly, giving a high mutual conductance.

While I have indicated the preferred embodim ents of myinvention ofwhich I am now aware and have also indicated only one specific applica- 7 tion for which my invention may be employed,

it will be apparent that my invention is by no means limited to the exact forms illustrated or the useindicated, but that many variations may be L made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is: o

1. An electron discharge device having a cathode, an anode and a grid positively biased with respect to ,said cathode positioned between said cathode and anode, a negatively biased grid positioned between the positively biased grid and cathode, and a third and fourth grid positioned between the positively biased grid and the anode at a potential not greater than cathode potential, the spacing between the cathode, anode and grids and the voltages applied to the electrodes being such that a virtual cathode is formed between the third and fourth grids.

2. An electron discharge device having a cathode and anode, and a positively biased grid between said cathode and anode, a negatively biased grid' positioned between the positively biased grid and the cathode, and third and fourth grid between said positively biased grid and anode at a potential not greater than that of the cathode,

the ratio of the spacing between the cathode, the

successive grids and the anode in succession from the cathode being of the order of l, 2, 2, 4 and 2. 3. An electron discharge device including a cathode and anode and at least four successive grids between said cathode and anode, the ratio of spacing of the electrodes in succession from the cathode being of the order of 1, 2, 2, 4 and 2.

4. An electron discharge device including a cathode and anode and at least four successive grids between said cathode and anode, the ratio of spacing of the electrodes in succession'from the cathode being of the order of 1, 2, 2, 4 and 2, the third and fourth successive grids from the cathode being electrically connected together and to said'cathode.

5. An electron discharge device including a cathode and anode and at least four successive grids between saidcathode and anode, means for applying a negative bias to the first successive grid from said cathode and means for applying 'a positive voltage to the second successive grid from the cathode and other means for maintaining the third and fourth successive grids from the cathode at a potential not greater than that of the cathode, the potentials applied to said grids and to the anode and the spacing between the cathode, grids and anode being such that a virtual cathode is formed between the third and fourth grids.

6. An electrondischarge device including a cathode and anode and at least four successive grids between said cathode and anode, the ratio of spacing of the electrodes in succession from the cathode being of the order of 1, 2, 2,

.4 and 2, means for biasing the first successive grid from the cathode negatively with respect to the cathode and. the second successive grid from the cathode positive with respect to the cathode, and means for maintaining the third and fourth grids at a potential not greater than that of the cathode, and means for applying a positive voltage to said anode.

7. An electron discharge device including a cathode and anode and at least four successive grids between saidcathode and anode, the ratio of spacing of the electrodes in succession from the cathode being of the order of 1, 2, 2, 4 and 2, means for biasing the first successive grid from the cathode negatively with respect to the cathode and the second successive grid from the cathode positive with respect to the cathode, and means for applying a positive voltage to said anode, and means for electrically connecting the third and fourth grids to said cathode.

8. An electron discharge device including a cathode and anode and at least four successive grids between said cathode and anode, the spacing between the third and fourth successive grids from the cathode being at least as great as the spacing between the cathode and the first successive grid from the cathode, means for biasing the first successive grid negatively with respect to the cathode and the second successive grid positive with respect to the cathode, means for maintaining the third and fourth grids at a potential not greater than that of the cathode, and means for applying a positive voltage to said anode, the potentials on the grids and anode being so adjusted that a virtual cathode is formed in the space between the third and fourth grids.

9. An electron discharge device including a cathode, an anode and at least four successive grids between said cathode and anode, the spacing between said third and fourth successive grids from the cathode being substantially four times the spacing between the cathode and the first successive grid from the cathode, means for biasing the first successive grid negative with respect to the cathode and means for biasing the second successive grid from the cathode positive with respect to the cathode, and other means for maintaining said third and fourth grids at I a potential not greater than that of the cathode,

and means for applying a positive voltage to the anode greater than that applied to the second successive grid.

10. An electron discharge device including a cathode, an anode, and at least two successive grids between the anode and the cathode, the spacing between the grid adjacent the anode and the anode being large with respect to the spacing between said grid and the cathode, and means for maintaining the anode and the grid adjacent the anode at such positive potentials and the grid adjacent the cathode at such lower potential that a change in potential of the grid adjacent the cathode in the negative direction causes an increase in anode current.

11. An electron discharge device including a cathode, an anode, and at least three successive grids between the anode and the cathode, the spacing between the third grid from the cathode and the anode being large with respect to the spacing between the first grid from the cathode and the cathode, and means for maintaining the anode and the second grid from the cathode at such positive potentials and said first grid and third grids at such lower potentials that a change in the first grid potential in the negative direction causes an increase in anode current and that a change in third grid potential in a negative direction causes a decrease in anode current.

12'. An electron discharge device including a cathode, an anode, and at least four successive grids between cathode and anode, and means for maintaining the second grid from the cathode and the anode at such positive potentials and the first, third and fourth grids from the cathode at such lower potentials that a change in potential of said first grid in a negative direction causes an increase in the anode current and that a change in the fourth grid potential in a negative direction causes a decrease in anode current.

13. An electron discharge device including a cathode and anode and at least four successive grids between the cathode and anode, thethird and fourth grids from the cathode being spaced from each other a greater distance than the distance between the cathode and the first grid from the cathode, means for maintaining the first, third and fourth grids from the cathode at potentials substantially the same as the cathode potential and means for maintaining the second grid from the cathode and the anode at such positive potentials that a change inpotential of said first grid in a negative direction causes an increase in the anode current. 7

14. An electron discharge device including a cathode and an anode and at least four successive grids between the cathode and the anode, the third and fourth grids from the cathode being spaced from each other a distance of not less than twice or more than five times the distance between the cathode and the first grid from the cathode, the first gridv from the cathode and second grid fro-m the cathode being spaced from each other a distance substantially the same as the distance between the second grid from the cathode and the third grid from the cathode, means for maintaining the first grid at a negative potential with respect to the oathode and means for maintaining the second grid from the cathode and the anode at such positive potentials that a change in potential on said first grid in the negative direction causes an increase in the anode current.

15. An electron discharge device including a cathode and anode and at least four successive grids between the cathode and anode, means for maintaining the second grid from the cathode and anode at such positive potentials and the first, third and fourth grids from the cathode at such lower potentials that a change in potential of said first grid in a negative direction causes an increase in the anode current, the first, third and fourth grids from the cathode each being adaptedto have separate control voltages applied thereto.

16. An electron discharge device including a cathode and anode and at least four successive grids between the cathode and anode, means for maintaining the second grid from the cathode and anode at such positive potentials and the st, third and fourth grids from the cathode at such lower potentials that a change in potential of said first grid in a negative direction causes an increase in the anode current, said second grid being adapted to provide an output electrode for said electron discharge device,

BROWDER J. THOMPSON. 

